Hitherto, a crane of this sort has been known as disclosed in Japanese Patent Application Laid-Open No. 1-313202 in which is proposed a travelling crane equipped with an elevator cab. In this prior art arrangement, the travelling crane includes a travelling body comprising a lower frame guided by a lower guide rail, an upper frame guided by an upper guide rail, and a pair of posts, front and rear, integrally connecting the two frames, and a carriage upward and downward movable between the two posts, with load transfer means mounted on the carriage.
A pair of guide rails, right and left, are mounted through a bracket to one of the posts on the outer side thereof as viewed from the direction of travel of the travelling body. An elevator cab is upward and downward movably carried on the guide rails and is equipped with brake means operable to act on the guide rails. Within the lower frame at a level below the posts there are provided a motor and a reduction gear for driving the elevator cab to move upward and downward, with a vertical run drive chain trained between a toothed drive wheel mounted to an output shaft of the motor or reduction gear and a toothed driven wheel disposed in the upper frame, the vertical run drive chain being connected to the elevator cab.
According to such prior art arrangement, the travelling crane can, when manually operated by an operator getting on a carriage-side cab or remotely operated from the ground side, perform load delivery to or load withdrawal from a target site of the rack through a combination of horizontal run of the travel body, vertical run of the carriage, and forking movement of load transfer means.
The elevator cab is used when emergency repairs are required due to, for example, a failure of the carriage or a load collapse occurring during the operation of the crane, as well as for regular maintenance and checkup purposes. In such a case, an operator gets on the elevator cab and manipulates a control panel provided in the cab to drive the motor to rotate the vertical drive chain forward and reverse, whereby the elevator cab will be moved upward and downward along the guide rail. When the elevator cab is brought to a stop at a position opposite to the carriage, the operator transfers from the elevator cab to the carriage to carry out the required repairs and/or maintenance and checkup work.
If the vertical run drive chain should become ruptured, the braking means, provided in opposed relation to the guide rails, will operate for braking action thereby to prevent the elevator cab from falling. The braking means is such that cam faces of brake elements act on flat surfaces of the guide rails, the cam faces being formed as serrated circumferential faces.
In the above described prior art arrangement, there is no provision of foothold or handle available for use by the operator in helping him transfer from the elevator cab to the carriage. This prevents such a transfer from being made in an easy and safe manner and even involves some danger in the case of such transfer at an elevated position.
The operation of the elevator cab for upward and downward movement is carried out via the control panel in the cab. The elevator cab has a window formed in its wall, which window provides only a narrow field of view because of the fact that the elevator cab is of a vertically rectangular box shape. Especially where the elevator cab is of such construction that its width or transverse length is further reduced, the one post obstructs the view from the window of the cab to the extent that there is available little field of view longitudinal of the path of movement of the travelling body, which does not permit any smooth and accurate operation of the cab for upward and downward movement. Where the elevator cab is so constructed that it has a larger transverse length to provide a wider field of view through its window, the cab is naturally larger in size and weight and, in addition, it will involve increased cost of operation of the travel crane per se because operation of the cab requires operation of the crane in conjunction therewith despite the fact that the elevator cab is used only occasionally.
In such arrangement wherein the elvator cab has a larger transverse length intended for provision of a wider field of view, it is not easy to operate the cab for upward and downward movement through the control panel while paying attention to the status of upward or downward movement of the cab, because the control panel is located away from the window. The elevator cab is usually positioned at its lowermost position and, therefore, an elevator cab having such a larger transverse length will substantially occupy the space between the travelling body and the rack, which does not permit easy passage of the elevator cab through that space.
The motor and the like for driving the elevator cab to move upward and downward are located within the lower frame, and the vertical run drive chain is trained about toothed driven wheels in the upper frame in a loop pattern. Therefore, the total length of the vertical run drive chain is about twice the length of the post. This results in greater shocks caused upon the elevator cab being started or brought to a stop, and results further in greater stretching of the chain due to the load applied (which, in this case, means the own weight of the elevator cab including the weight of the operator). Thus, the elevator cab is forced to get abruptly bounced (or subject to abrupt vertical jolting) when it is started or brought to a stop. The fact that the vertical run drive chain is of such a large length is disadvantageous in respect of cost. Furthermore, the fact that the motor and reduction gears are disposed within the lower frame does not permit easy maintenance and checkup.
Installing the pair of guide rails, right and left, to be acted upon by the brake means involves the steps of fixing a plurality of brackets to the post and fixing the guide rails between the upper and lower brackets. Further, additional fixing operations, such as welding, are required at a number of locations. As such, the operations involved in the installing work are very laborious to complete and are costly. Moreover, two sets of braking means are required and this further complicates the arrangement of the elevator cab as a whole. Another problem is that when, at each time of braking, the circumferential serrated portions act on flat surfaces of the guide rails, the circumferential serrated portions will bite into the respective guide rail surfaces to mar the guide rails, which eventually may lead to the braking elements being damaged including the circumferential serrated portions.